Hi,
we had this issue, too, in earlier version. I think, you should upgrade.
Another option would be direct DB manipulation, but this will probably lead to an inconsistent DB:
In the table ezuser_user (or similar), you'll probably find your "tux" user. When you delete it from this table (or just change the login name from "tux" to "tux_old"), ez should be able to create a new "tux" user. You'll need some MySQL client for this, of course (command line mysql or phpMyAdmin will do fine).